Weak magnetic flux leakage: A possible method for studying pipeline defects located either inside or outside the structures

Magnetic leakage distribution results from linear defects of oil-gas pipelines in a weak magnetic field, which is modeled by the magnetic dipole theory. The analysis is useful for the identification of defects located either inside or outside the pipelines. The results indicate that the radial signals of inside-outside defects can be clearly distinguished, and the axial signals are basically the same in a weak magnetic field. The theoretical and the experimental results are very consistent.